1. Field of the Invention
The present invention relates to an image pickup apparatus, such as a digital still camera and a digital video camera, a lens apparatus, and an image pickup system.
2. Description of the Related Art
A conventionally known lens interchangeable type camera system includes an image pickup apparatus (camera body) configured to provide image pickup processing, lens control, and image recording, and a lens apparatus configured to drive a lens and a diaphragm in accordance with a control command from the camera body. A smooth lens control is particularly required in capturing a motion image and in displaying the live view in synchronization with an image pickup cycle, and it is thus necessary to synchronize the image pickup timing of the camera body with the control timing of the lens apparatus. Hence, the lens apparatus controls driving of the image pickup optical system in synchronization with the control reference signal (synchronizing signal) provided from the camera body.
When the camera body changes the cycle of the control reference signal, it is necessary to avoid asynchronous state between the camera body and the lens apparatus. Accordingly, WO2009/139173 discloses a method of switching the cycle of the control reference signal by an advance notice of switching of the cycle from the camera body to the lens apparatus, by informing the camera body through the lens apparatus that the lens apparatus is ready to change the cycle, and by switching the cycle of the control reference signal in the camera body.
However, when the camera body sends an inquiry to the lens apparatus before switching the cycle of the control reference signal as in the method of WO2009/139173, switching takes a long time. Switching of the cycle of the control reference signal may be caused by an operation of an operator. In that case, the responsiveness and the operability may be sacrificed. In addition, the camera body needs to process the operation of the operator at the cycle of the current control reference signal until the cycle is switched, and when multiple processing tasks occur, communication processing delays and the cycle of the control reference signal cannot be maintained. Of course, when the camera body immediately changes the cycle of the control reference signal, the lens apparatus cannot follow the cycle and the malfunction may occur. For example, the lens apparatus smoothly moves a lens according to a moving speed calculated based upon a current position, a target position, and the cycle of the control reference signal in the motion image pickup. When the camera suddenly shortens the cycle of the control reference signal while the lens apparatus is moving the lens, the lens apparatus loses control of moving the lens to the target position within the shortened cycle.